1. Field of the Invention
This invention is directed to an improved fuel injection valve for an internal combustion engine.
2. Description of the Prior Art
A fuel injection valve for internal combustion engines of the type with which this invention is concerned is known for instance from German Patent Disclosure DE 196 18 650 A1. Such a fuel injection valve has a valve body, in which a bore is embodied. A pistonlike valve member is disposed longitudinally displaceably in this bore and on its end toward the combustion chamber has a valve sealing face, which cooperates with a valve seat embodied on the end of the bore toward the combustion chamber. The valve member is surrounded by a pressure chamber embodied in the valve body, and this pressure chamber can be filled with fuel at high pressure and extends as far as the valve seat. At least one injection opening is embodied in the valve seat, which connects the bore and thus the pressure chamber with the combustion chamber of the engine. By means of a longitudinal motion of a valve member, the valve member with its valve sealing face lifts from the valve seat, causing the pressure chamber to communicate with the injection openings. The valve seat is embodied essentially conically, and the tip of the cone forming the conical face is oriented toward the combustion chamber. The valve sealing face of the valve member is correspondingly embodied conically as well, and the valve sealing face has two conical faces with different angles of inclination, so that at the transition between these two conical faces, a sealing edge is formed. In the closing position of the valve member, or in other words when the valve sealing face is resting on the valve seat, this sealing edge is pressed into the valve seat, so that secure sealing off of the pressure chamber from the injection openings is possible.
The valve member is acted upon by a device with a closing force that presses the valve member onto the valve seat. Because of the hydraulic pressure in the pressure chamber, the valve member experiences a force acting in the axial direction, which force is oriented counter to the closing force. If the pressure in the pressure chamber exceeds an opening pressure, then the hydraulic force on the valve member becomes greater than the closing force, and the valve member moves out of its closing position, away from the valve seat. The magnitude of this opening pressure depends, among other factors, on what the diameter of the sealing edge at the valve seat is. A change in the opening pressure causes a change in the injection characteristic of the injection valve, so that for optimal injection, an at least approximately constant opening pressure is indispensable. The known fuel injection valve has the disadvantage in this respect that the sealing edge formed by the transition between the two closing faces is beaten into the valve seat over the course of operation of the fuel injection valve, causing the hydraulically effective sealing line diameter to change over time, and hence the opening pressure does not remain constant. Particularly in modern fuel injection systems, which are optimized for low pollutant emissions, this is a major disadvantage.